1. Field of the Invention
The present invention relates to a method for driving a so called dot matrix memory type AC plasma display panel which has shown remarkable recent progress in use for example in personal computers, office work stations, and also wall televisions etc. for which future development is expected.
2. Description of the Related Art
In general, a plasma display panel is featured by thin construction, no flicker and a large display contrast ratio. Moreover it has many features, namely that a relatively large screen is possible, response speed is fast, and a multi-color luminescence is also possible by using a spontaneous light emission type fluorescent body. Therefore, recently this is becoming widely used in the field of computer related display devices and in the field of color image displays.
For this plasma display panel, depending on the operating method thereof, there is an AC type device operated indirectly in an AC discharge state with an electrode coated with a dielectric substance, and a DC type operated in a direct discharge state with an electrode exposed to a discharge space. Furthermore for the AC type, there is a memory operating type which uses a memory of a discharge cell for a drive method, and a refresh operating type which does not use this. The luminance of the plasma display panel is proportional to the number of discharges, that is the number of repetitions of the pulse voltage. In the case of the above refresh type, if the display capacity becomes large, luminance is reduced and therefore it is mainly used in plasma display panels with small display capacity.
FIG. 1 is a cross-section showing an example of the construction of one display cell of an AC memory operating type plasma display panel. This display panel comprises two insulating boards 101 and 102 constituting a rear face and a front face, both of which are made of glass, a transparent scanning electrode 103 and a transparent sustaining electrode 104 formed on the insulating board 102, trace electrodes 105 and 106 arranged so as to lie on the scanning electrode 103 and the sustaining electrode 104 in order to lower resistance of the electrode, a data electrode 107 formed orthogonal to the scanning electrode 103 and the sustaining electrode 104, a discharge gas space 108 filled with discharge gas including helium, neon and xenon or a mixed gas thereof disposed between the insulating boards 101 and 102, a partition 109 for maintaining this discharge gas space 108 and dividing into display cells, a phosphor 111 for converting ultraviolet rays generated by discharge of the discharge gas to visible light 110, a dielectric film 112 covering the scanning electrode 103 and sustaining electrode 104, a protecting layer 113 composed of magnesium oxide or the like for protecting the dielectric film 112 against discharging, and a dielectric film 114 covering the data electrode 107.
The drive operation of a plasma display panel of such a construction, will be explained with reference to FIG. 2. Period 1 is a pre-discharge (priming) period. A pre-discharge pulse Ppr-s applied to the scanning electrode side, and a pre-discharge pulse Ppr-c applied to the sustaining electrode side are rectangular waves. In the pre-discharge period, by means of the rectangular wave of positive polarity applied to the scanning electrode, and the rectangular wave of negative polarity applied to the sustaining electrode, pre-discharge occurs in the discharge gas space near the inter-electrode gap of the scanning electrode and the sustaining electrode of all cells. Then, simultaneous with the formation of active particles which facilitate the occurrence of cell discharge, a wall charge of a negative polarity is attached to the scanning electrode, and of a positive polarity is attached to the sustaining electrode. The discharge in this case is a strong discharge form.
Period 2 is a pre-discharge erasing period. A pre-discharge erasing pulse Ppe is applied which gradually reduces the wall charge attached to the scanning electrode and the sustaining electrode in the pre-discharge period, and the waveform thereof becomes a waveform where the scanning electrode side decreases slowly with negative polarity.
Period 3 is a scanning period. Writing discharge is generated in the cell which is selected by the scanning pulse Pw of negative polarity applied to the scanning electrode and the data pulse Pdata of positive polarity applied to the data electrode, and a wall charge is attached to the cell at a location where light is emitted in the subsequent sustaining period. The writing discharge only occurs at the intersection point of the scanning electrode to which the scanning pulse Pw is applied and the data electrode to which the data pulse Pdata is applied. When discharge occurs, the wall charge is attached to that part. On the other hand, in the cell where discharge has not occurred, the wall charge is not attached.
Period 4 is a sustaining period. Starting from the sustaining electrode side, the positive polarity sustaining pulses Psus-s, Psus-c to be alternately applied to the subsequent scanning electrode side and sustaining electrode side, are applied to the scanning electrode and the sustaining electrode. At this time the wall charge is attached to the cell which is selectively written in the scanning period, and the negative polarity sustaining pulse voltage and the wall charge voltage are superposed, so that the minimum discharge voltage is exceeded and discharge occurs. The wall charge is arranged so that when this discharge occurs, the voltages applied to the respective electrodes are cancelled. Consequently, a negative charge is attached to the sustaining electrode, and a positive charge is attached to the scanning electrode. Since the next sustaining pulse is a pulse where the scanning electrode side is a negative voltage, then due to superimposing with the wall charge, the effective voltage applied to the discharge space exceeds the discharge starting voltage so that discharge occurs. Thereafter, the same situation is repeated to sustain the discharge. On the other hand, in the cell where writing discharge has not occurred the wall charge is extremely small. Therefore, even if a sustaining pulse is applied, a sustaining discharge does not occur.
In the conventional technology, the pre-discharge erasing pulse becomes a negative polarity pulse with a gradual fall. If the sum of the negative charge accumulated in the scanning electrode by the pre-discharge, and the applied voltage of the pre-discharge erasing pulse exceeds the minimum discharge starting voltage, discharge occurs. In this case, since the falling of the pulse is gradual, the discharge becomes a weak discharge form, and the wall charge is reduced to the level where the discharge starting voltage is slightly lower, and the discharge converges. Weak discharge is repeated until waveform variations of the subsequent pre-discharge erasing pulses cease.
In this discharge, even if the pulse reaches the finally attained voltage, since the discharge is intermittent for a while, the undesirable situation results where the wall charge at the pulse completion time does not become constant, so that the settable range for the subsequently applied scanning pulse and the sustaining pulse is narrow. Due to the nonuniformity of the wall charge, the required voltage distribution for the writing discharge and the sustaining discharge becomes wide, and erroneous lighting due to the erroneous discharge occurs.
It is an object of the present invention to provide a method for driving a stabilized plasma display where distribution of the erroneous discharge starting voltage is narrow, so that the erroneous discharge of the scanning period and the sustaining period is reduced.
In order to address the above problem, a first aspect of the invention is a method for driving a plasma display panel characterized in that after a potential change of a pre-discharge erasing pulse, a pre-discharge erasing voltage holding time is inserted This is so that, by providing the voltage holding time after the pre-discharge erasing pulse has gradually fallen, there is convergence of the weak discharge which continues even after the potential fluctuations of the pre-discharge erasing pulse have converged, so that erasing is possible until the residual wall charge amount becomes constant.
Moreover, a second aspect of the invention is a method for driving a plasma display panel characterized in that a scanning pulse voltage is greater than a finally attained voltage and a holding voltage of a pre-discharge erasing pulse. Since the wall charge corresponding to the potential difference of the finally attained voltage of the pre-discharge erasing pulse and the scanning pulse voltage, is superimposed on the scanning pulse voltage, it is possible to reduce the data voltage and the scanning voltage.
Furthermore, a third aspect of the invention is a method for driving a plasma display panel characterized in that a pre-sustaining erasing period is inserted between a scanning period and a sustaining period. As a result, in the case where a writing discharge does not occur in the scanning period, the residual wall charge can be erased, so that the erroneous discharge due to superposition of the residual wall charge and the sustaining voltage can be reduced.
Moreover, a fourth aspect of the invention is a method for driving a plasma display panel according to the first aspect, characterized in that the pre-discharge erasing voltage holding time is greater than 5 microseconds. This is because the time until convergence of the weak discharge which continues even after potential fluctuations of the pre-discharge erasing pulse have converged, is approximately 5 microseconds. As a result, even in the case where the discharge characteristics for each of the cells are different, the amount of wall discharge can be made constant, giving a drive method of high reliability.
Furthermore, a fifth aspect of the invention is a method for driving a plasma display panel, characterized in that a potential change in a pre-sustaining erasing voltage is gradual. As a result, the discharge of the wall charge is performed as a weak discharge, so that attachment of a charge of an opposite sign to that of the electrode after completion of discharge which occurs at the time of forced discharge, does not occur.
Moreover, a sixth aspect of the invention is a method for driving a plasma display panel characterized in that a pre-sustaining erasing voltage holding time is inserted after a potential change of the pre-sustaining erasing voltage in the pre-sustaining erasing period. As a result, since a sustaining discharge is not performed until convergence of the weak discharge which occurs in the pre-sustaining erasing voltage change, the residual wall charge can be made constant.
Furthermore, a seventh aspect of the invention is a method for driving a plasma display panel, characterized in that the pre-sustaining erasing voltage holding time is greater than 5 microseconds. This is so that the time until convergence of the weak discharge which continues even after potential fluctuations of the sustaining pre-discharge voltage have converged, is around 5 microseconds, and in order to uniformly erase the residual wall charge.